Continuous tobacco sheet production



y 1956 w. G. FRANKENBURG ET AL 2,747,583

CONTINUOUS TOBACCO SHEET PRODUCTION Filed Sept. 8, 1955 IN V EN TORS' WALTER G. FRANKENBURG ALFRED M. GOTTSCHO BY Wm AGENT United States Patent CONTINUOUS TOBACCO SHEET PRODUCTION Walter G. Frankenburg, Millersville, and Alfred M. Gottscho, Lancaster, Pa., assignors to General Cigar Co., Inc., New York, N. Y-., a corporation of New York Application September 8, 1953, Serial No. 378,722

11 Claims. (Cl. 131-140) This invention relates to the continuous manufacture of thin tobacco sheets in the form of extensive strips or ribbons.

For a period of at least fifty years there have been numerous proposals for the conversion of tobacco leaves into sheets that might be used in machines for the production of cigars and like smoking products, thereby minimizing manual labor. However, none of these proposals has ever achieved commercial success for the reason that the process for converting tobacco leaves into a sheet material invariably altered the original smoking characteristics of the tobacco to an extent that the resulting tobacco product was no longer acceptable to smokers. Recent developments have completely changed this situation since, as disclosed in U. S. Patent 2,592,553, granted April 15, 1952, to W. G. Frankenburg and P. W. Garbo, and U. S. Patent 2,592,554, granted April 15, 1952, to W. G. Frankenburg, it has been discovered that tobacco leaves in dry form may be pulverized and the tobacco powder admixed with highly viscous aqueous solutions of innocuous binding agents to form a tobacco paste which may be spread in thin layers and dried to yield thin tobacco sheets having essentially the smoking character- .istics of the original tobacco leaves.

The success of these recent developments which make it commercially possible to convert tobacco leaves into thin tobacco sheets has created the need for an economical and continuous process by which the tobacco paste is spread into thin layers that are then quickly and uniformly dried to provide tobacco sheets in extensive ribbon form.

Accordingly, a principal object of this invention is to provide a continuous, rapid process for converting tobacco paste into thin tobacco sheets of extensive length.

Other objects and advantages of this invention will be apparent from the description which follows.

In accordance with this invention, a tobacco paste, which preferably is prepared in accordance with the teachings of U. S. Patents 2,592,553 and 2,592,554, is deposited as a thin layer on a moving belt and conveyed through a drying zone in which the wet layer is contacted by a flow of heated and relatively dry air. The temperature, relative humidity and quantity of the air brought into contact with the wet layer of tobacco paste while passing through the drying zone are correlated with the thickness of the layer and the velocity of its travel through the drying zone so that upon emerging from the drying zone the layer is in the form of a coherent film or sheet. Inasmuch as the finished tobacco sheet in most instances has a thickness of less than 0.010 inch, it is well to note that the drying of the tobacco paste is controlled in the drying zone to avoid such thorough drying that the resulting tobacco sheet will lose all of its adhesion to the conveying belt and be blown away from the belt by the flow of the heated air used to effect drying. In short, the drying conditions are correlated so that the tobacco sheet issuing from the drying zone, while being substantially dry to visual inspection, will generally still contain 2 ing under hood 26. The amount of drying effected in approximately 12 to 22% by weight of water, At this stage, the tobacco sheet has considerable adhesion to the conveying belt and, in view of its thinness, is susceptible to tearing and rupture when the finished tobacco sheet is stripped from the conveying belt. For this reason, finely atomized water is brought into contact with the exposed top surface of the tobacco sheet while still on the conveying belt and this water quickly penetrates the thin sheet with the result that its adhesion to the belt is very considerably weakened, thus ensuring that the sheet can be stripped from the supporting belt without tearing.

For a better understanding of the invention, the further description will refer to the accompanying drawing which diagrammatically illustrates a preferred embodiment of the invention.

An aqueous tobacco paste is supplied through pipe 10 to a reverse roll coater which, as is well known, comprises a casting roll 12 and a parallel doctor roll 14. The tobacco paste is dropped into the nip between rolls 12 and 14 and is laterally retained on these rolls by end plates 16 which fit around rolls 12 and 14. A wiper blade 18 keeps the paste from being carried away by rotating doctor roll 14 from its position between rolls 12 and 14. There is a small spacing at the nip 20 between rolls 12 and 14 which is adjustable to give the thickness of tobacco paste that is desired for transfer to endless conveyor belt 22. The desired layer of tobacco paste carried down from nip 21) by casting roll 12 is transferred to belt 22, which preferably is a stainless steel belt, at the point 24 where roll 12 contacts belt 22. The layer of' tobacco paste transferred to belt 22 is then conveyed through drying hoods 26 and 28 from which the deposited layer emerges as a coherent tobacco sheet. Drying hood 26 comprises a fan or blower 30, a dust filter 32 and a steam coil 34 so that the air blown into hood 26 may be warmed to the desired temperature before contacting the layer of tobacco paste passing under hood 26. It is advisable to have the warmed air impinge on the layer of tobacco paste in the form of a plurality of small, high-velocity streams or jets which may be achieved by having a perforated or slitted wall 36 along the bottom of hood 26, spaced a small distance, say about 2 inches, above conveyer belt 22. Additional details for this type of drying hood are disclosed in U. S. Patent 1,157,149, granted October 19, 1915, to H. M. Conger. Drying hood 28 is similarly provided with a blower 38, filter 40, steam coil 42 and apertured bottom plate 44. Additionally, hood 28 is provided with a spray or fogging nozzle 46 through which water may be injected into the warmed air to control its relative humidity before coming into contact with the layer of tobacco paste conveyed by belt 22 through hood 28.

While it is possible to effect drying of the tobacco paste in a single drying zone, it has been found preferable to use at least two successive drying zones for the reason that initially the wet paste may be contacted with air warmed to a temperature as high as 160 F. provided the exposure of the paste to such temperature is for not more than of the order of one minute. Preferably, the temperature of the warmed air in hood 26 is in the range of to F. The relative humidity of this warmed air should not exceed about 25%. Thus, the major portion of the water in the tobacco paste is rapidly evaporated while the layer travels under hood 26. Further drying of the layer is effected while passing under hood 28 which supplies a flow of air warmed to a temperature about 10 to 15 F. lower than the temperature of the air in hood 26 but not lower than 110 F. and having a relative humidity in the range of l2to 25%. The time of drying under hood 28 is substantially equal to the time of dry- 3 hoods 26 and 28 is controlled so that the layer issuing from hood-28is visually dry and very largely still adhering to conveying belt 22. At this stage, the tobacco sheet will on an average have a residualmoisture content of about '12 to, 22% by weight. To facilitate stripping of the adherent tobacco sheet, it, has been foun'dthat the addition of a Very 'small quantity of water in the form of a fine mist or fog not only will loosen the bond between the tobacco sheet and conveying belt 22 but also will render thetobacco sheet more pliable so that it may be rolled up without cracking or tearing. It is surprising that the moisture content'of the tobacco sheet which can be readily stripped from conveying belt 22 is only in the range of 25 to 40% by weight. A fogging nozzle 48 is disposed above belt 22 so as topermit a fine water mist to'fsettle downon the tobacco sheet before it is stripped from belt 22. The thus moistened or conditioned tobacco sheet '50 is looped around idler rolls 52 and54 and wound up as a roll 56.

In an illustrative operation of the processes already described in connection with the attached drawing, the

tobacco paste is prepared by admixing 8.5 pounds of pulverized tobacco with 69 pounds of an aqueous solution of methyl cellulose (4,000 centipoise type) containing 2% by weight of the methyl cellulose. Additionally, the tobacco paste contains 0.1 pound of fine glass fibers, 2.2 pounds. of plasticizer, 0.7 pound of diatomaceous earth and 07 pound of siliceous catalyst of the type disclosed in the copending application of W. 'G. Frankenburg, Serial No. 105,660, filed July 19, 1949, now U. S. Patent 2,706,695, granted April 19, 1955. 'The homogeneous aqueous paste is carried by casting roll 12 through an opening of about 0.012 inch at nip 20 between rolls 12 and 14 and transferred to stainless steel belt- 22 at point 24 where casting roll 12 contacts belt 22. The layer of tobacco paste on belt 22 travels at a velocity of 3.9 feet per minute and is subjected to a plurality of fine streams of air which has been warmed in hood 26 to a temperature of approximately 137 F. The relative humidity of this air is approximately 20%. The distance of travel of the layer of tobacco paste under hood 26 is 7.5 feet. The partially dried layer then passes under hood 28 which is also 7.5 feet long and is there contacted with multiple streams of air warmed to a temperature of about 125 F. and having a relative humidity of about 16%. Upon issuing from hood 28, the layer is visually dry but still very largely adherent to conveying belt 22 and has a residual-moisture content of about 15% by weight. In passing under the fine water mist provided by nozzle 48, the moisture content of the to-' bacco sheet is raised to approximately 27% by weight and the adhesion between the tobacco sheet and belt 22 is thus weakened to the p'ointthat the sheet is readily stripped from belt 22by looping it around idler rolls 52 and 54 and applying a gentle winding force to the spool or roll 56 of finished tobacco sheet. The thus produced tobacco sheet has an average thickness of about 0.003 inch;

The processof this invention is especially adapted for the continuous production of thin tobacco sheets from aqueous pastes of pulverized tobacco and water-soluble binding agents, particularly cellulose ethers and alginates as disclosed and claimed'in U. S. Patents 2,592,553 and 2,592,554. As already mentioned, the finished tobacco sheets will in most instances have an average thickness of not more than 0.010 inch and rarely as much as 0.015

inch. Where the tobacco sheet is to be utilized in the manufacture of cigars, itsaverage thickness will generally be in the range of about 0,002; to'0.004 inch which closely approximatesthe thickness ofa tobacco leaf. The thickness of the tobacco paste asorig'mally deposited .onthe movingbelt will be considerably greater than that-of the finished sheet, owing to the large quantity, of water present in-the paste. in; manyinstances, the thicknessof the layer ,of tobacco. pasteapplied, to the conveyer beltwill 4 be on the order of five times that of the finished tobacco sheet.

The moisture contents of the tobacco sheets as produced by this invention are determined by placing samples of the tobacco sheets for one hour in an oven in which there is a circulation of air having a temperature of C. and measuring thel'os's of weight of the samles.

p In view of the various modifications of the invention which will occur to those skilled in the art upon consideration of the foregoing disclosure without departing from the spirit or scope thereof, only such limitations should be imposed as are indicated by the appended claims.

What is claimed is:

l. A continuous process for the production of a thin, coherent tobacco sheet of extensive length, which comprises spreading a thin layer of an aqueous paste containing pulverized tobacco and an innocuous water-soluble binding agent on the surface of an endless conveyor belt, impinging said layer on said belt with a flow of air warmed to a temperature in the range of to F. and having a relative humidity of not more than 25% for a period effective for the evaporation of a major portion of the waterin said layer, subsequently impinging said layer on said belt, while stillwarm from the preceding impingement with warmed air, with a flow of air warmed-to a temperature about 10 to 15 F. lower than the first-mentioned temperature and having a relative humidity in the range of 12 to 25 for a period eifective for the-further evaporation of water in said layer until said layer is converted intoa visually dry and coherent tobacco sheet adherent to said belt, moistening the adherent tobacco sheet'with a flne water mist until said sheet appears uniformly dampened, stripping the dampened sheet from said belt, and rolling up the stripped, dampened sheet.

2. The continuous process of claim 1 wherein each of the two mentioned flows of warmed airimpinges on the exposed surface of said layer on said belt as multiple, closely spaced streams.

3. The continuous process of claim 1 wherein the aqueous paste is made by admixing a minor weight proportion of pulverized tobacco with a preponderant weight pro portion of water containing approximately 2% by weight of a cellulose ether dissolved therein as the, binding agent and said aqueouspaste is spread as a thin layer not more than about 0.0l2' inch in thickness. on the conveyer belt.

4. The continuous process of" claim 1 wherein the visually dry and coherent tobacco sheetadherent to said belt has a moisturecontent in the range of about 12 to 22% by weight and the dampened sheet has a moisture thin layer of an aqueous paste containing pulverized tobacco and an innocuous water-soluble binding agent, impinging a flow 'ofwarm'ed air having a temperature-up to F. anda relative humidity ofnot more than about 25% on said layer for a predetermined period of time to warm and partiallydry said layer, impinging on the thus" warmed and partially dried layer another flow of warmed air having a temperature at'least 10 F. below the firstmentioned temperature but not below .110 F. for a perind of time substantially equalto said predetermined period so that said'partially dried layer is convertedinto a visin'illy-dry and coherent tobacco sheet adherent to said belt,- and' stripping said coherent tobaccosheet from said belt after remoistening said coherent tobacco sheet.

7.'The continuous process of claim 6 wherein eachof the'two mentioned" flows of warmed air impinges onthe exposed surface of said layer on said belt as multiple, closely spaced streams.

8. The continuous process of claim 7 wherein the aqueous paste is made by admixing a minor weight proportion of pulverized tobacco with a preponderant Weight proportion of water containing approximately 2% by weight of methyl cellulose dissolved therein as the binding agent.

9. A continuous process for the production of a thin, coherent tobacco sheet of extensive length, which cornprises spreading a thin layer of an aqueous paste containing pulverized tobacco admixed with an innocuous binding agent on the surface of an endless conveyer belt, impinging said layer on said belt with a flow of air warmed to a temperature up to 160 F. and having a relative humidity of not more than 25% for a period efiective for the evaporation of a major portion of the water in said layer, subsequently impinging said layer on said belt, while still warm from the preceding impingement with warmed air, with a fiow of air warmed to a temperature at least 10 F. lower than the firstmentioned temperature but not below 110 F. for a period efiective for the further evaporation of water in said layer until said layer is converted into a visually dry and coherent tobacco sheet adherent to said belt, and stripping said coherent tobacco sheet from said belt after remoistening said coherent tobacco sheet.

10. The continuous process of claim 9 wherein each of the two mentioned flows of warmed air impinges on the exposed surface of said layer on said belt as multiple, closely spaced streams.

11. The continuous process of claim 9 wherein the aqueous paste is made by admixing a minor weight proportion of pulverized tobacco with a preponderant weight proportion of water containing approximately 2% by weight of a cellulose ether dissolved therein as the binding agent and said aqueous paste is spread as a thin layer not more than about 0.012 inch in thickness on the conveyer belt.

References Cited in the file of this patent UNITED STATES PATENTS 1,157,149 Conger Oct. 19, 1915 1,568,316 Buensod Ian. 5, 1926 2,105,848 Touton Jan. 18, 1938 2,433,877 Wells Jan. 6, 1948 2,475,568 Moore July 5, 1949 2,592,553 Frankenburg Apr. 15, 1952 2,656,841 Gurley Oct. 27, 1953 FOREIGN PATENTS 497,773 Belgium Sept. 15, 1950 1,026,418 France Feb. 4, 1953 

